Nitrogen adsorption on Nb2C6H4+ cations: the important role of benzyne (ortho-C6H4)

Abstract

N₂ adsorption is a prerequisite for activation and transformation. Time-of-flight mass spectrometry experiments show that the Nb₂C₆H₄⁺ cation, resulting from the gas-phase reaction of Nb₂⁺ with C₆H₆, is more favorable for N₂ adsorption than Nb⁺ and Nb₂⁺ cations. Density functional theory calculations reveal the effect of the ortho-C₆H₄ ligand on N₂ adsorption. In Nb₂C₆H₄⁺, interactions between the Nb-4d and C-2p orbitals enable the Nb₂⁺ cation to form coordination bonds with the ortho-C₆H₄ ligand. Although the ortho-C₆H₄ ligand in Nb₂C₆H₄⁺ is not directly involved in the reaction, its presence increases the polarity of the cluster and brings the highest occupied molecular orbital (HOMO) closer to the lowest occupied molecular orbital (LUMO) of N₂, thereby increasing the N₂ adsorption energy, which effectively facilitates N₂ adsorption and activation. This study provides fundamental insights into the mechanisms of N₂ adsorption in “transition metal–organic ligand” systems.